Phytofluene structure

A great diversity in molecular structure is observed among herbicides which inhibit carotene biosynthesis as is exemplified by the structures of norflurazon, fluridone and difunone (shown below). Nonetheless, many of these compounds, which comprise a subset of the larger group known as bleaching herbicides, appear to inhibit the same step in the biosynthetic pathway to the carotenoids (1 ). The inhibited step is the desaturation of 15-cis phytoene to 15- cis phytofluene (Figure 1) and the build-up of phytoene in plants and in cell-free systems which have been treated with these herbicides is well documented (2-4). 

Several phytoene desaturases are known that differ in the number of desaturation steps and in their structures. Among them, the bacteriaPfungal type is encoded by crti, and the cyanobacterial/algal/plant type is encoded by crtP or pds. Phytoene desaturase converts phytoene to -carotene with phytofluene as an intermediate. The reaction is stimulated by NAD, NADP, and oxygen. 

Fig. 11. The pathway of conversion of phytoene to lycopene. In this pathway trans structures are shown for all compounds. In plants the first two compounds in this pathway (phytoene and phytofluene) have a central 15,15 -cis double bond. An isomerization reaction converts cis-phytofluene to trans-phytolluene in plants.

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